This invention relates to thermosettable resin compositions and their preparation. In a specific embodiment, the invention relates to cyanate ester resins having improved toughness and processable melt viscosity.
Advanced composites are high-performance materials made up of a fiber-reinforced thermoplastic or thermosettable polymer. Thermosettable polymers useful in advanced composites applications must meet a set of demanding requirements, including good high-temperature properties, such as high (above 200.degree. C.) cured glass transition temperature, and good mechanical strength. For ease of processing in preparing prepregs for composite parts, the uncured material ideally has a low (below 120.degree. C.) melting temperature and low viscosity in the melt.
Cyanate ester resins have low melt viscosity and good high-temperature properties, but cyanate ester homopolymers are quite brittle. Addition of thermoplastics or cyanate-terminated oligomers increases the toughness but produces uncured mixtures so high in viscosity that fiber impregnation and processing by standard thermoset techniques are difficult.
It is therefore an object of the invention to provide cyanate ester resins which have low uncured melt viscosity and improved toughness in the cured state.